Biodecolorization of Paper Mills Wastewater Using Anaerobic Composting

Abstract

This research studied the feasibility of using anaerobic composting for decolorizing effluents in the pulp and paper industry. While color is regarded as an aesthetic problem, there are several adverse effects associated to it. The effects include reduced sunlight penetration, increases in water temperature, and decreases in dissolved oxygen. In addition, color is often associated with carcinogens. These problems along with stricter regulations have lead to increase research in this area. In this research, we studied a new method for reducing color using anaerobic composting. Biologically active and gamma-sterilized compost was used to study the biological and abiotic adsorption and decolorization kinetics to demonstrate the feasibility of removing color from paper mill effluents using anaerobic composting. The results showed that higher decolorization was achieved using active compost in comparison with gamma sterilized compost.

The second set of experiments studied color removal sustainability and the degree and rate of decolorization of effluents of dissimilar color, pH, and oxidation reduction potential levels. More than 75% color reduction was achieved for effluents having color as high as 90,000 Platinum Cobalt Units. When the samples were aerated, the color reversion was minimal. The third part of this research presents experiments done to investigate the best conditions for biodecolorization. The parameters studied include compost-to-feed ratio, length of sequencing batch reactor cycles, mixing and shaking, temperature, flocculent effects, long-term operation, and nutritional requirements. The optimized conditions were applied to pilot scale reactors and decolorization exceeding 90% was achieved. The interaction between different anaerobic microbial communities was studied in the fourth part of this research. The results show that inhibition of sulfur reducing bacteria resulted in higher decolorization. An unknown culture was isolated and its 16S rRNA gene was sequenced for identification. This analysis resulted in 82.1% identity with Aeromonas punctata. Color reduction of 55% was achieved using A. punctata without additional sources of carbon. The last part of the research studied chromophores fate in the biodecolorization process using size exclusion chromatography. Treatment of the effluents showed that polymerization and biodegradation took place. In general, the results from this study presented a novel, feasible, and readily implementable method of removing color using compost biosolids. The use of this process not only serves to decrease effluents color but will also reduce the treatment of solid waste by reusing waste fibers from the paper manufacturing industry. As new regulations for the color levels in effluents emerge, mills may focus on using this process to treat low-volume, high color wastes to make processing more economical.